1. Field of the Invention
This invention relates generally to reciprocating piston type internal combustion (I.C.) engines for motor vehicles. More specifically it relates to I.C. engines having variable compression ratio pistons and connecting rods.
2. Background Information
A gasoline engine whose compression ratio remains invariant as operating conditions change is said to be knock-limited. This means that the compression ratio built into the engine design must be selected to avoid objectionable engine knock that would otherwise occur during certain conditions of engine operation if the compression ratio were larger. However, those conditions that give rise to engine knocking in a motor vehicle typically prevail for only limited times as the vehicle is being driven. At other times, the engine could operate with better efficiency, and still without knocking, if the compression ratio could be made higher, but unfortunately the engine is incapable of achieving more efficient operation during those times because its compression ratio cannot change.
Certain technologies relating to reciprocating piston I.C. engines having variable compression ratio pistons and connecting rods are disclosed in various patents, including U.S. Pat. Nos. 1,875,180; 2,376,214; 4,510,895; 4,687,348; 4,979,427; 5,562,068; and 5,755,192. Various reasons for employing such technologies in I.C. engines have been advanced in those documents. One reason is to improve efficiency by enabling an engine that is relatively more lightly loaded to run at a compression ratio that is higher than a compression ratio at which the engine operates when running relatively more heavily loaded.
The compression ratio of an engine can be varied by varying the overall effective length of a connecting rod and piston. Change in overall effective length may be accomplished in either the connecting rod, or the piston, or in both. The foregoing patents describe various mechanisms for varying overall effective length.
The present invention relates to further improvements in construction of connecting rods and pistons in reciprocating piston I.C. engines for varying engine compression ratios as engine operating conditions change. Various embodiments of the invention are disclosed.
According to a first disclosed embodiment, a variable length piston and connecting rod assembly for imparting a variable compression ratio to an internal combustion engine comprises a first part and a second part that are coupled by a variable length mechanism that is captured between the parts, wherein the variable length mechanism comprising a frustoconical spring washer, and an elastomeric mass disposed against a concave face of the washer.
According to a second disclosed embodiment, a variable length piston for imparting a variable compression ratio to an internal combustion engine comprises a first part and a second part that are coupled by a variable length mechanism. The first part comprises a head and a stem extending from a central region of the head, and the second part comprises a surface with which the stem of the first part has a telescopic fit. An elastomeric mass is captured between confronting surfaces of the first and second parts surrounding the stem.
According to a third disclosed embodiment, a variable length piston and connecting rod assembly for imparting a variable compression ratio to an internal combustion engine comprises a first part and a second part that are coupled by a variable length mechanism that is captured between the parts. The first part comprises a blind hole, and an elastomeric mass comprising a ring is disposed in the blind hole. A first piston comprising a head is disposed in the blind hole above the elastomeric ring and has a stem that passes through the ring. A second piston comprising a head is disposed in the blind hole above the head of the first piston. A closure closing the blind hole captures the heads of the pistons but comprising a central through-hole, and the second piston comprising a stem that passes from its head through the closure through-hole to attach to the second part. An elastomeric mass is captured axially between the second part and the closure.
According to a fourth disclosed embodiment, a variable length piston and connecting rod assembly for imparting a variable compression ratio to an internal combustion engine comprises a first part and a second part that are coupled by a variable length mechanism that is captured between the parts. The first part comprises a blind hole, and an elastomeric mass is disposed in the blind hole. A piston is disposed in the blind hole above the elastomeric mass, and a closure closes the blind hole to capture the piston but comprises a central through-hole. The second part passes through the closure through-hole to attach to the piston. Oil passages supply oil to, and return oil from, a space in the blind hole below the elastomeric mass.